1. Field of the Invention
This invention relates to a method of manufacturing a permanent magnet with R(T.sub.1-y M.sub.y).sub.z, as the chief components, wherein R denotes one or two species of rare earth metals, including Y, T denotes transition metals, principally Fe or Fe and Co, M denotes metalloid elements, principally B, and wherein 0.02.ltoreq.y.ltoreq.0.15, and 5.ltoreq.z.ltoreq.9.
2. Description of Prior Art
Since it was discovered that, among the rare earth transition metal alloys, intermetallic compounds having a 2:17 ratio of rare earth metals to transition metals theoretically possess very high magnetic properties [(BH) max-50 MGOe], various attempts have been made to obtain practical permanent magnet alloys with compounds of the above system as the chief component.
For example, the high magnetic property of (BH) max-30 MGOe was achieved with an intermetallic compound of the Sm-Co-Cu-Fe system and that of (BH) max-40 GOe with an intermetallic compound of the Nd-Fe system. These composite alloys were generally manufactured by processes used for sintered permanent magnets, i.e., pulverizing, compression-molding while oriented in a magentic field or compression molding in a non-magnetic field, and sintering, melting and aging.
The conventional methods for obtaining fine particles include the mechanical pulverizing of ingots, the rough pulverizing by hydrogenation of ingots to cause brittleness in a high pressure hydrogen atmosphere followed by fine pulverizing upon dehydrogenation, and (as shown in U.S. Pat. No. 4,585,473), the forming of a spherical crude power of about 100 .mu.m by spraying the melt substance with an inert gas atomization technique and further mechanical pulverization to the desired particle size.
However, in the case of fine pulverization of alloys with the composition shown by the general formula R(T.sub.1-y M.sub.y).sub.z, wherein R denotes one or two species of rare earth metals, including Y, T denotes transition metals, principally Fe or Fe and Co, M denotes metalloid elements, principally B, and wherein 0.02&lt;y&lt;0.15, and 5&lt;z&lt;9, the powder formed by mechanically pulverizing ingots effectively produces magnetically aligned solids during the subsequent oriented compression-molding in a magnetic field.
In the case of using gas atomization techniques, although they are advantageous in their simple processing, minute crystals of 0.1-10 .mu.m are magnetically formed at random in each grain during the rapid solidification following atomization. Consequently, there were shortcomings such that, unless the minute crystals are pulverized to less than 1 .mu.m in the subsequent fine pulverization process, a high degree of orientation is not achieved during molding in a magnetic field, resulting in a permanent magnet with an inferior angularity of the demagnetization curve. Furthermore, another shortcoming is that the sintering temperature, which normally ranges between 1000.degree.-1200.degree. C., causes the final magnet to be completely sintered, thus making the formation process difficult.